1. Field of the Invention
The present invention relates to transmission means, and more particularly, to a transmission line interface circuit.
2. Description of the Prior Art
In the art of industrial process control, it is common for a process sensor together with its transmitter to be located at a significant distance from a central control room. It is also common for the sensor/transmitter to be energized by a power source located at the control room. In order to provide reliable transmission of data from the sensor to the control room, communication between the control room and the remote sensor/transmitter is by way of a two-wire transmission line. It would be preferable, for several reasons, if both the energizing power supply and the transmitter were to be grounded. However, since so-called ground potential may not be the same for two widely separated instrumentalities, a simple ground connection at such two widely separated instrumentalities would tend to produce an error in the analog data transmitted.